Nitrofurantoin, an effective urinary antiseptic, is associated with serious lung toxicity. Recent studies indicate that nitrofurantoin can induce the generation of toxic O2-derived species such as superoxide, hydrogen peroxide, and the hydroxyl radical. We have developed a unique in vitro model of nitrofurantoin lung toxicity which indicates these toxic O2-derived species are lethal to susceptible lung cells; however, the actual cellular mechanism of how drug-induced oxidants injure lung cells remains unclear. To clarify possible cellular mechanisms of toxicity, we will test the hypotheses that nitrofurantoin-generated oxidants result in a depletion of cellular antioxidants and a loss of calcium homeostasis. Specific Aims will utilize the in vitro model developed in our laboratory to assess the effect of nitrofurantoin on cultured human pulmonary endothelial cells to: 1) deplete intracellular glutathione (monitored by an HPLC method), 2) initiate a lethal rise in free cytosolic calcium (3 methods of determination including fura-2, aequorin and phosphorylasle-a), 3) cause the appearance of characteristic cell surface "blebs" (scanning electron microscopy), and 4) result finally in the irreversible injury of the cell (51Cr cytotoxicity assay). To assess if each of these steps are linked in a causal relationship, we will next modulate the oxidant burden to the cell and GSH levels in the cell to determine if we successfully modulate later steps in the proposed pathogenetic scheme (e.g., changes in cytosolic calcium etc). If successful, this would support the validity of this hypothesis; if not, the hypothesis may be denied. Furthermore, we will study other human lung cell populations to determine if pulmonary endothelial cells are more susceptible to the drug, and possibly to suggest possible mechanisms to account for these differences. Successfull results may suggest fundamentally new concepts in the pathogenesis of acute lung injury. An improved understanding of nitrofurantoin lung toxicity may permit development of future therapeutic strategies which can significantly reduce the morbidity and mortality associated with this latrogenic lung disorder.